I'm new to electronics after having my interest piqued while being introduced to Arduinos and programming at large. Wanted to get deeper in the discrete components and build out some minimal skills to do diagnostics and testing. In line with that, I have slowly accumulated a few basic instruments, and had been keeping my eye out for a scope. As luck would have it, I saw one posted locally on Craigslist, and I went over to pick it up untested for $60. Luckily for me, it also included the hard copy service manual, which I have been fawning over as I admire the schematics.
Quick summary of the scope:
Good overall condition. A little grimy on the outside and on the front panel, but inside is very clean. A review of the knobs and buttons reveal that all actuate well, except for the "line" (on/off). Luckily for me it is stuck in the ON position, so I am turning the scope on via the power cord.
First power on, I got a single point cycling across the screen. I probed the 1v cal and saw a good, flat square wave.
Then things got a little funky. I was waiting for one of the cheapo assemble it yourself signal generators to show up in the mail, so I didn't really have anything fun to do with the scope. But for the next couple of days I couldn't see anything on the screen. When I would turn up the beam intensity, the left side of the screen would start bleaching out green. Then I would press the beam find, I would suddenly see a dot on the left half of the screen. My gut was telling me I had an issue with my horizontal.
This afternoon, I got home and decided to start probing the horizontal controls as it went into the gun. At some point I looked at the display and saw I had proper functionality, but that would come and go. Sometimes it would decide not to show anything, and I would switch between displays and time/div settings and poke at the horizontal control boards and by luck it would turn back on. I'm attaching some pictures from today to show that I encountered.
First set is a sine wave, then the beam find while the function was applied. I'd be interested to hear from folks if I should expect to see the wave come back over itself on the right side as it shows.
Second set is the cal square wave, then the beam find while the cal was applied. Similar question as above.
The third set is what I would encounter when I would be unable to see a signal. I would apply the cal wave, not see anything, and then press the beam find and see a vertical line. My assumption is that it proves that I am getting good vertical, but intermittently not getting horizontal.
Lastly, at very small increments of time/div, I am seeing what I would best characterize as back trace. It isn't happening all the time, and the back trace is generally softer than the main trace, but I gather its not supposed to be there.
As far as general operations, the trace strikes me as a bit faint. I will change the time/div and, especially when they are very small units, it will take a bit for the line to come into focus, or may require that I apply additional brightness to make it out.
I'd be interested to know if folks had any gut instincts on the matter before I start digging around randomly (which is about the best outcome, despite having access to the manual). My plan is to review the schematic and try to plot a course to diagnose the issues further. I have also procured deoxit to clean the time/div contacts. I tested the LVPS and am seeing good measurements per the manual. I don't have the probe needed to dive into the HVPS.